Regional and Hemispheric Influences on Temporal Variability in Baseline Carbon Monoxide and Ozone over the Northeast...

Interannual variability in baseline carbon monoxide (CO) and ozone (O₃), defined as mixing ratios under minimal influence of recent and local emissions, was studied for seven rural sites in the Northeast US over 2001 - 2010. Annual baseline CO exhibited statistically significant decreasing trends (-4.3 - -2.3 ppbv yr^-1), while baseline O₃ did not display trends at any site. In examining the data by season, wintertime and springtime baseline CO at the two highest sites (1.5 km and 2 km asl) did not experience significant trends. Decadal increasing trends (~2.55 ppbv yr^-1) were found in springtime and wintertime baseline O₃ in southern New Hampshire, which was associated with anthropogenic NO_x emission reductions from the urban corridor. Biomass burning emissions impacted summertime baseline CO with ~38% variability from wildfire emissions in Russia and ~22% from Canada at five sites and impacted baseline O₃ at the two high elevation sites only with ~27% variability from wildfires in both Russia and Canada. The Arctic Oscillation was negatively correlated with summertime baseline O₃, while the North Atlantic Oscillation was positively correlated with springtime baseline O₃. This study suggested that anthropogenic and biomass burning emissions, and meteorological conditions were important factors working together to determine baseline O₃ and CO in the Northeast U.S. during the 2000s.